The objective of this study was to develop a musculoskeletal model incorporated with a subject-specific knee joint to predict the tibiofemoral contact force (TFCF) during daily motions. For this purpose, 18 healthy participants were recruited to perform the motion data acquisition using synchronized motion capture and force platform systems, and motion simulation based on an improved musculoskeletal model for five daily activities, including normal walking, stair ascent, stair descent, sit-to-stand, and stand-to-sit. The proposed musculoskeletal model included subject-specific models of bones, cartilages, and meniscus, detailed knee ligaments and muscles, deformable elastic contacts, and multiple degrees of freedom (DOFs) of the knee joint. The prediction accuracy was demonstrated by the good agreements of TFCF curves between the model predictions and in vivo measurements for the five activities (RMSE: 0.216~0.311 BW, R2: 0.928~0.992, and CE: 0.048~0.141). Based on the validated model, the TFCF on total, medial, and lateral compartments (TFCFTotal, TFCFMedial, and TFCFLateral) during the five daily activities were predicted. For TFCFTotal, the peak force for stair descent or sit-to-stand was the largest, followed by stair ascent or stand-to-sit, and finally normal walking. For TFCFMedial, stair descent had the largest peak, followed by stair ascent. There were no significant differences between the peak TFCFMedial values of normal walking, sit-to-stand, and stand-to-sit. For TFCFLateral, the peak of sit-to-stand was the largest, followed by stand-to-sit or stair descent, and finally normal walking or stair ascent. This study is valuable for further understanding the biomechanics of a healthy knee joint and providing theoretical guidance for the treatment of knee osteoarthritis (KOA).

Surface electromyographic (sEMG)-based motion recognition has been successfully applied in the exoskeleton, human-machine interaction, and rehabilitation engineering. To improve the accuracy of motion recognition and then achieve accurate control of the exoskeleton, this paper is devoted to proposing a one-dimensional (1D) convolutional neural network (1D-CNN) to classify seven daily lower-limb motions from the eight main muscles of human lower limbs. The proposed model architecture mainly consisted of three 1D convolutional layers, three max-pooling layers, and one global average pooling layer. The Teager-Kaiser energy operator was adopted for the starting and ending points detection of sEMG signals. To avoid overfitting, only two features (i.e., mean absolute value (MAV) and root mean square (RMS)) were extracted in this study and used as the input of the proposed model. The results show that the accuracy of motion recognition based on our proposed model had been improved to more than 97.0 +/- 0.8% and was higher than that based on the deep neural network (DNN) and support vector machine (SVM) models (95.0 +/- 0.6% and 92.8 +/- 0.7%). The research results and proposed model of this study are significant for research into exoskeleton control based on sEMG signals.

Objective: This study aim to quantify the differences in knee biomechanics during gait between knee osteoarthritis (KOA) patients and healthy individuals. Methods: Twenty KOA patients (4 males and 16 females, 66.2 +/- 7.7 years) and twenty controls (16 males and 4 females, 64.8 +/- 5.4 years) were recruited for gait test using the motion capture system and force-platform system. The spatiotemporal parameters, knee kinematics and kinetics, and tibiofemoral contact force (TFCF) were calculated using an improved musculoskeletal model. Results: KOA patients walked with reduced speed (48.6 %), stride length (32.9 %), stride height (33.0 %), time proportions of single-support phases (19.2 %), increased gait cycle time (31.0 %), time proportions of stance (8.5 %) and double-support phases (57.7-75.9 %). KOA patients had significant smaller peak flexion angle (29.1 %), flexion ROM (50.6 %) and peak flexion moment (90.2 %), greater peak adduction moment (KAM) (40.7 %), peak rotation moments (KRM) (50.0 %), KAM impulse (106.2 %) and KRM impulse (126.0 %). In proximodistal direction, greater medial TFCF impulse (238 %), total and medial first-peak TFCF (9.6 % and 15.2 %), and smaller lateral peak TFCF (33.3 %) and TFCF impulse (38.4 %) were found in KOA patients. Besides, significant differences were found in the total, medial and lateral peak TFCFs and TFCF impulses in mediolateral direction, and the medial and lateral TFCFs and TFCF impulses in anteroposterior direction. Conclusions: Significant differences were found in the spatiotemporal parameters, knee kinematics and kinetics, and TFCF between the two groups. The results of this study have important implication for clinicians and rehabilitation physicians. These quantified biomechanical differences can provide data support for the personalized and quantified rehabilitation strategies, give suggestions for the exercises of KOA patients, help monitor disease, evaluate surgical treatment, and develop more effective preoperative planning and postoperative rehabilitation strategies.

Background:Running has been widely recognized as a beneficial activity for improving physical fitness, but it can also increase the risk of running-related injuries (RRIs). This study aims to assess the impact of long-term running on the structural and biochemical composition of the knee. Methods:This study recruited a total of 32 participants, including 16 male recreational runners, aged 28-49 years, with a running experience of 2-7 years, and 16 matched sedentary controls. Magnetic resonance (MR) scans of T2* mapping and three-dimensional double-echo steady-state (3D-DESS) were performed on all participants. The volumes, thickness, and T2* values of joint articular cartilage were obtained via automatic segmentation software. Results:Compared with the sedentary controls, runners exhibited significant increases in the volumes of both the femoral medial articular cartilage and the tibial medial articular cartilage. Additionally, there were significant increases in the thickness of several cartilage regions, including femoral medial cartilage, femoral medial articular cartilage, femoral medial thickness, femoral lateral cartilage, and tibial medial articular cartilage. Notably, the T2* values in the femoral lateral and tibial lateral cartilage of runners decreased significantly, while those in the patellar cartilage and medial tibial cartilage increased significantly. Runner pace was negatively correlated with the overall knee cartilage thickness (r=-0.556; P=0.02), femoral cartilage thickness (r=-0.533; P=0.03), and volume (r=-0.532; P=0.03) but positively correlated with the T2* value of the patellar cartilage (r=0.577; P=0.01). Conclusions:Our study suggests that long-term mechanical stress from running may lead to increased thickness and volume in certain knee joint cartilage regions, possibly enhancing the functional adaptability of knee cartilage. The varying changes in T2* value in the tibial and fibular cartilage areas may indicate differing adaptability to pressure.

This article aims to evaluate the service life of a steam drum in a power plant by conducting internal boiler inspections and combining existing fatigue life assessment methods and standards. Based on the evaluation results, targeted maintenance and preventive measures have been proposed, providi

Accurate prediction of tibiofemoral contact force (TFCF) during daily living activities is significant for understanding the initiation, progression, and treatment of knee osteoarthritis (KOA). However, the diversity of target activities, prediction accuracy, and computational efficiency of the current musculoskeletal simulations need to be further improved. In this study, a subject-specific musculoskeletal model considered the tibiofemoral alignment, medial-lateral contact locations, secondary tibiofemoral and all patellofemoral motions, and knee ligaments was proposed to predict the TFCFs during the five daily activities (normal walking, sit-to-stand, stand-to-sit, stair ascent, and stair descent) in OpenSim software. The standing lower-limbs-full-length radiograph, local radiograph of knee joint, motion capture data, and force plate data of eighteen subjects were acquired as the input data of the musculoskeletal model. The results showed good agreements of TFCFs between the predictions based on our proposed musculoskeletal model and the in-vivo measurements based on instrumented knee implants during the five daily activities (RMSE: 0.16 similar to 0.31 BW, R-2: 0.88 similar to 0.97, M: -0.11 similar to -0.02, P: 0.03 similar to 0.10, and C: 0.04 similar to 0.14). Additionally, the order of the peak total and lateral TFCFs from low to high was normal walking, stair ascent and stand-to-sit, and stair descent and sit-to-stand (P < 0.05), and the peak medial TFCF was stand-to-sit, sit-to-stand, normal walking, stair ascent and stair descent (P < 0.05). The outcomes of this study are valuable for further understanding the knee biomechanics during daily living activities and providing theoretical guidance for the treatments of KOA.

Background. Valgus braces are prescribed as a common conservative treatment option for patients with medial gonarthrosis to improve their quality of life. Many studies had reviewed the effects of the valgus braces on patients with medial gonarthrosis, while they mainly focused on the knee adduction moment (KAM), with less attention paid to other parameters such as spatiotemporal and morphological parameters. Objectives. The purpose of this study was to review the effects of valgus braces on the spatiotemporal, kinematic/kinetic, morphological, and muscle parameters. Methods. Based on the selected keywords, a survey of literatures was performed in Web of Science, PubMed, Scopus, and Google Scholar using the PRISMA methods, and the search period was established from January 2000 to March 2022. Results. Thirty-four articles were included. According to the conclusion of these articles, the valgus brace can be used to relieve the symptoms of patients with medial gonarthrosis by decreasing the varus angle, decreasing the KAM, and redistributing the knee compartment loads. However, the effects of valgus braces on other biomechanical parameters (e.g., walking speed, cadence, joint angle, and joint space) had not reached a consensus. Conclusions. The valgus knee brace can effectively relieve the symptoms of medial gonarthrosis through multiple mechanisms, while there is still some confusion about the effectiveness of the valgus brace on the other biomechanical parameters.

Muscle fatigue, as a serious social problem, affects the performance of daily living activities, especially for workers. Decrease of movement control ability caused by muscle fatigue is one of the risk and intrinsic factors for occupational accidents, such as slips, trips, falls, etc. In order to reduce the accident rate and optimize the existing prevention measures, it is necessary to investigate the effect of fatigue on kinematics, kinetics, and muscle activities of human body. In this paper, 26 healthy participants were recruited. The kinematics and kinetics analysis of lower limb joints, and surface electromyograms (sEMG) time-domain and frequency-domain analysis of lower limb periarticular muscles were utilized to investigate the effects of muscle fatigue. The results showed that the fatigue reduced the range-of-motion (RoM) of the lower limb joints. Smaller plantarflexion, knee flexion and hip flexion angles, and greater dorsiflexion angles were observed after fatigue. For the joint moment, the fatigue did not alter the joint moments except for the smaller knee flexion moment. For the joint power, the fatigue decreased the generation power of ankle, knee and hip joint and the absorption power of ankle and knee joints, whereas increased the absorption power of hip joint. Besides, the fatigue increased the normalized integrated sEMG (iEMG) and root-mean-square (RMS) of sEMG, and shifted the median frequency (MF) and mean power frequency (MPF) of sEMG toward lower frequencies. The results from the present study concluded that the muscle fatigue changed the kinematics, kinetics and muscle activities of lower limbs during gait, and then could increase the risk rate of occupational accidents.

Malalignment of the lower limbs is the main biomechanical factor for knee osteoarthritis (KOA). The static hip-knee-ankle angle (S-HKAA) measured from radiograph is regarded as the "gold standard" of the malalignment. However, many evidences showed that the S-HKAA has no significant correlation with the knee dynamic-load distribution, unlike the dynamic HKAA (D-HKAA). The purpose of this study was to quantitatively analyze the D-HKAA and investigate the relationship between D-HKAA and S-HKAA for both KOA and healthy participants. In this paper, twenty-five healthy subjects and twenty-five medial compartment KOA (M-KOA) patients were recruited. Three-dimensional motion analysis and standing lower-limbs-full-length radiograph were utilized to obtain the D-HKAA and S-HKAA, respectively. The results showed that the mean D-HKAA was more varus than the S-HKAA (p<0.05). For the mean D-HKAA, larger varus angle was observed in swing phase than stance phase (p<0.05). Compared with healthy subjects, the M-KOA patients had remarkably smaller S-HKAA and D-HKAA during gait cycle (p<0.01). For the relationship between the S-HKAA and mean D-HKAA, no significant correlation was found for both healthy subjects and M-KOA patients (r<0.357, n=25, p>0.05, Spearman correlation analysis). In conclusion, the S-HKAA was limited to predict the D-HKAA for both M-KOA patients and healthy subjects. The D-HKAA should be given more attention to the orthopedist and the designer of knee brace and orthotics.

SUMMARY It was reported that about 10% of people suffer from painful knee arthritis, and a quarter of them were severely disabled. The core activities of daily living were severely limited by knee osteoarthritis (KOA). In order to reduce knee pain and prolong the life of the knee joint, there has been an increasing demand on the development of exoskeletons, for prevention and treatment. The course of KOA was closely related to the biomechanics of knee joint, and the pathogenesis was summarized based on the biomechanics of knee joint. For the prevention and clinical treatment, exoskeletons are classified into three categories: prevention, treatment, and rehabilitation after the operation. Furthermore, the design concepts, actuators, sensors, control strategies, and evaluation criteria were presented. Finally, the shortcomings and limitations were summarized. It is useful for researchers to develop suitable exoskeletons in the future.

Studying the principles of human gait is the center of many research studies. In order to analyze and predict the movement of the human walking, the lower extremity of human body is assumed to be a rigid connecting-rod model due to the physiological structure of human body, and the connecting rods are assumed to be connected by joints. Based on the assumptions, a rigid five-bar connecting-rod model of human body in the sagittal plane is developed, and the five rigid rods represent the torso, left thigh, right thigh, left calf, right calf, respectively. Then, mathematical equations of the kinematics and dynamics for human walk on level ground are derived. Since in this study the model is considered as a planar model, only the motion in the sagittal plane is studied. The results from the experiments are compared with the computer simulation results to verify the rigid five-bar linkage model, and the gait information can be predicted effectively by the kinematic and dynamic models.

Knee dysfunction, such as knee osteoarthritis, meniscus injury, ligament injury, spinal cord injury and stroke, considerably impacts the normal living ability and mental health of these patients. Developing more effective knee assistive devices is in urgent need for effectively recovering their motion capabilities and improving their self-living activities. In this paper, we review and discuss the mechanical system design, sensing and control systems design, and performance evaluation of the main research advances in knee assistive devices. Firstly, in order to clearly illustrate and compare the mechanical system design, the mechanical system design is classified into four components to discuss: human attachment design, joint alignment design, actuation design and power transmission design. Then, the sensing and control systems design, which includes human biological signals based control systems, human–device interaction signals based control systems and device signals only based control systems, is compared and discussed. Furthermore, the performance evaluation methods and effectiveness of most of the knee assistive devices are reviewed. Finally, a discussion of the existing problems in the current studies and some recommendations for future research are presented.

The knee joint, as the main lower limb motor joint, is the most vulnerable and susceptible joint. The knee injuries considerably impact the normal living ability and mental health of patients. Understanding the biomechanics of a normal and diseased knee joint is in urgent need for designing knee assistive devices and optimizing a rehabilitation exercise program. In this paper, we systematically searched electronic databases (from 2000 to November 2019) including ScienceDirect, Web of Science, PubMed, Google Scholar, and IEEE/IET Electronic Library for potentially relevant articles. After duplicates were removed and inclusion criteria applied to the titles, abstracts, and full text, 138 articles remained for review. The selected articles were divided into two groups to be analyzed. Firstly, the real movement of a normal knee joint and the normal knee biomechanics of four kinds of daily motions in the sagittal and coronal planes, which include normal walking, running, stair climbing, and sit-to-stand, were discussed and analyzed. Secondly, an overview of the current knowledge on the movement biomechanical effects of common knee musculoskeletal disorders and knee neurological disorders were provided. Finally, a discussion of the existing problems in the current studies and some recommendation for future research were presented. In general, this review reveals that there is no clear assessment about the biomechanics of normal and diseased knee joints at the current state of the art. The biomechanics properties could be significantly affected by knee musculoskeletal or neurological disorders. Deeper understanding of the biomechanics of the normal and diseased knee joint will still be an urgent need in the future.

Human motion intention recognition is a key to achieve perfect human-machine coordination and wearing comfort of wearable robots. Surface electromyography (sEMG), as a bioelectrical signal, generates prior to the corresponding motion and reflects the human motion intention directly. Thus, a better human-machine interaction can be achieved by using sEMG based motion intention recognition. In this paper, we review and discuss the state of the art of the sEMG based motion intention recognition that is mainly used in detail. According to the method adopted, motion intention recognition is divided into two groups: sEMG-driven musculoskeletal (MS) model based motion intention recognition and machine learning (ML) model based motion intention recognition. The specific models and recognition effects of each study are analyzed and systematically compared. Finally, a discussion of the existing problems in the current studies, major advances, and future challenges is presented.

Human-machine interaction is a key component in the wearable robotics field. Because surface electromyography (sEMG) generates prior to the corresponding motion and reflects the motion intention directly, sEMG-based motion intention recognition can achieve better human-machine interaction and has been widely used in recent years. However, most of the relevant researches are concentrated on the discrete-motion classification which can not be used for smooth control of wearable robots. Thus, in this paper, an improved feature-based convolutional neural networks (CNN) model was proposed for analyzing the sEMG-based continuous estimation of knee joint angle. The normal walking experiments with six sEMG channels acquired system and optical motion capture system were carried out to analyze actual and desired knee angle. The sEMG-based continuous-motion regressions of knee joint angle obtained by the proposed model and other two existing neural network models, i.e. original data-based CNN model and back propagation neural network (BPNN) model were calculated and compared with experimental ones. The results showed that the proposed model can predict knee angle with a higher level of accuracy compared to BPNN and original data-based CNN models.

Suture broken, knot slipping and tissue tearing are the main reasons of wound closure failure in clinical operation. Based on this, we simulated the suturing and healing operation by using a biological materials testing machine and investigated the tensile properties before and after knotting, relaxation property and friction property of three common sutures: silk, polyglactin 910 and polypropylene. Results show that the tensile property decreased after knotting. The tensile strength of polyglactin 910 and elongation of polypropylene were the largest. During the relaxation process, the sutures relaxed the most in the first 2 hours. The relaxation from less to more was: polyglactin 910, silk and polypropylene. Coating or monofilament could obviously reduce the surface roughness of sutures, and thus reduce the friction force of the suture-suture interface. The friction force of the suture-suture interface increased with the increasing load but did no change with the increasing velocity. The results can provide an important theoretical basis for the optimizations of suture design and knotting operation.

This paper researches on the effects of Reynolds number and mass flow ratio on the film cooling characteristics at high turbulence intensity (Tu = 15%). The experiment adopted an actual three-dimensional twisted vane and presents the film cooling characteristics on full-coverage film surface in a two-passage, linear cascade. The cooling effectiveness and heat transfer coefficient of the vane’s whole surface were obtained by using transient liquid crystal measurement technique. The transient liquid crystal is SPN/R35C1W, whose bandwidth is 2°C. There are fifteen rows of film cooling holes which have different diameter, injection angle and yaw angle. The secondary flow was supplied by two cavities. The front cavity supplied the secondary flow to thirteen rows of film cooling holes that were arranged in the suction surface, the leading edge and the front half of the pressure surface. The rear cavity supplied the secondary flow to the rear half of pressure surface which included two rows of film cooling holes. The investigated parameters are Reynolds number of 1 × 105, 1.3 × 105 and 1.6 × 105 and the mass flow ratio of MFR = 5.5%∼12.5% (6 cases). The data recorded in the experiment was analyzed with MATLAB. Results show that the combined effects of mass flow ratio and channel vortex are the maintain reasons that influence the distribution of cooling effectiveness in the contour. Increasing the mass flow ratio can improve the film cooling effectiveness on leading edge and pressure surface, while that presents complex rule on suction surface. Increasing the Reynolds number can improve the heat transfer coefficient at the same mass flow ratio. When increasing the mass flow ratio, the heat transfer coefficient increases on leading edge and pressure surface at Re = 1.6 × 105. However, the decreases at film hole outlet region on the suction side, and not obviously changes at the film hole downstream region.

In the process of surgical suturing, friction phenomena at the interface between sutures and tissues can seriously affect the suturing efficiency. However, few studies have assessed the detailed effects of types of sutures or tissues and stitching parameters on the friction behavior. In this paper, the different factors affecting the friction behaviors between sutures and tissues were studied. The unidirectional sliding wear mode in a line-on-flat configuration was selected to simulate the real surgical suturing by using a UMT-II Micro-Tribometer. Artificial skin, porcine muscle and porcine liver were used as experimental samples. Three different surface morphology and structure sutures: multifilament suture (silk), monofilament suture (prolene) and multifilament suture with coating (vicryl), were investigated in this study. The normal load was from 0.1 to 0.5 N, and the unidirectional sliding (suturing) speed was from 5 to 25 mm/s to simulate the suturing operation. Results showed that the friction coefficient at the suture–tissue interface decreased with the increase in normal load and increased with the increase in suturing speed due to the nonlinear viscoelasticity and deformation hysteresis of the soft tissues. The sutures with monofilament structure or coating could effectively reduce the friction coefficient of the suture–tissue interface. Compared to the artificial skin, the porcine tissues had the lower friction coefficients because of 30% blood and 17% interstitial fluid filled in liver and muscle, respectively, which acted as lubricants and reduced the adhesion friction coefficient of the suture–tissue interface. The results can provide guidance for the surgical suture manufacture and the surgical manipulation skills.